sync: TeeStringIO write should return int

Change-Id: I211776a493cad4b005c6e201833e9700def2feb9
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/390657
Reviewed-by: Mike Frysinger <vapier@google.com>
Commit-Queue: Daniel Kutik <daniel.kutik@lavawerk.com>
Tested-by: Daniel Kutik <daniel.kutik@lavawerk.com>

subcmds/sync.py

diff --git a/subcmds/sync.py b/subcmds/sync.py
index 2fea61d..9e43df4 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -185,9 +185,10 @@
 
     def write(self, s: str) -> int:
         """Write to additional destination."""
-        super().write(s)
+        ret = super().write(s)
         if self.io is not None:
             self.io.write(s)
+        return ret
 
 
 class Sync(Command, MirrorSafeCommand):